Soft Drinks and Weight Gain: How Strong Is the Link?

Emily Wolff, MPH; Michael L. Dansinger, MD, MS


Medscape J Med. 2008;10(8):189 

In This Article

Mechanisms by Which Soft Drinks May Promote Obesity and Related Diseases

There are 4 main mechanisms by which soft drinks may promote obesity and cardiovascular risk factors: direct caloric increases, appetite stimulation, adverse metabolic effects of high-fructose corn syrup consumption, and replacement of milk and other beneficial dietary intake.

Sugar-sweetened soft drinks typically contain 140-150 calories per 12-oz serving. If normal dietary intake decreased by an equivalent amount of calories per serving, then weight change would not be expected. However, as noted above, DiMeglio and Mattes[6] found that there was no decrease in usual dietary intake in response to 450 calories per day from sucrose-sweetened soda. (The daily caloric intake was equal to baseline intake plus the caloric intake attributed to the soda.) In the same study subjects, a solid sucrose supplement in the form of jelly beans was associated with a caloric reduction from baseline dietary intake that perfectly compensated for the caloric load provided by the jelly beans, such that the daily caloric intake remained unchanged. Others have reported similar findings.[38,39] Hypothetically, sugar solutions may fail to trigger satiety in the same way that solid preparations do; however, the physiologic mechanisms have not been fully determined.

Appetite stimulation associated with rapidly changing glucose and/or insulin levels may be caused by rapidly absorbed, high glycemic carbohydrates, including those found in sugar-sweetened soft drinks. A rapidly falling serum glucose level is a well-known appetite stimulant, and carefully conducted human studies have attributed increased hunger and caloric intake to differences in glycemic index or glycemic load intake, and associated differences in glucose and insulin levels.[40,41] The DiMeglio data described above may not support this hypothesis because the glycemic load of the jelly beans vs the soda was probably similar.[6]

Fructose, found in similar amounts in both sucrose and high-fructose corn syrup, may hypothetically promote obesity more than an equivalent amount of glucose. A study by Elliott and coworkers[42] examined the relationship between fructose, weight gain, and the insulin resistance syndrome and found that fructose, compared with glucose, is preferentially metabolized to lipid in the liver. In animal studies, fructose consumption induces insulin resistance, impaired glucose tolerance, hyperinsulinemia, hypertriacylglycerolemia, and hypertension, although data in humans are less clear.[42] Because fructose has limited insulin-stimulating effects, the consumption of foods and beverages that contain fructose produce smaller amounts of insulin than glucose-containing carbohydrates. In addition, because leptin production is regulated by insulin responses to meals, circulating leptin concentrations are reduced by the consumption of fructose. Bray and coworkers[13] have also found that the digestion, absorption, and metabolism of fructose differ from those of glucose, noting that when large amounts of fructose are ingested, the fructose provides a relatively unregulated source of carbon precursors for hepatic lipogenesis. Furthermore, a recent study conducted in mice suggested that the consumption of fructose-sweetened beverages increases adiposity more than the consumption of either sucrose-sweetened or artificially sweetened beverages.[43]

The consumption of milk has greatly decreased over the past few decades, whereas sugar-sweetened soft drink consumption has greatly increased. Energy intake from milk decreased by 38% between 1977 and 2001.[12] It has been shown that this trade-off between sweetened drinks and milk has led to a lower daily intake of protein, calcium, phosphorous, magnesium, zinc, and vitamin A at the highest level of sweetened drink consumption (> 2 glasses or 12 oz/day).[44] Harnack and colleagues[45] found similar results in children and adolescents, particularly at high levels of soft drink consumption. French and coworkers[4] also noted that soft drinks may affect the dietary quality of youth by displacing milk consumption, which can reduce calcium intake among children and increase their risk for osteoporosis and bone fracture. Nielsen and Popkin[12] have hypothesized that because dairy products may have a favorable effect on weight, reducing milk intake may be associated with increased weight gain, especially if the milk is being replaced with drinks of a higher caloric value. Popkin and colleagues,[46] however, citing the 2005 Dietary Guidelines for Americans, noted that there was no sufficient evidence that milk consumption reduced, or prevented, weight gain.


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